Portable Logging Bridges
Minnesota Lake Superior Area, MN

Grantee: Logging Educational & Resource Center
Basin Program Funds: $29,500
Non-federal Funds: $12,990
Project Duration: 07/2003 - 06/2005
Status: complete

Problem Statement
A critical source of stream sedimentation and erosion in logging operations are temporary stream crossings. During logging harvest, loggers have to cross streams on a regular basis. If the stream crossing is not protected, the equipment crossing the stream will cause sediment to enter the streams.

In the past, installing a culvert has been viewed as the primary option for stream crossings. The culvert option usually involves bringing in fill, which creates a potential sedimentation problem and it also narrows the stream flow.

Portable bridges have been found to be a desirable alternative in many cases, but most of these bridges have been for in-woods logging equipment, and not capable of supporting log trucks. This, in many cases, has limited their uses and has either resulted in use of culverts, or in construction of many miles of roads to access the timber from another direction. In many cases crossing a stream and keeping the access distance as short as possible is the best way to protect water quality, rather than create miles of road which exposes mineral soil to erosion and is much harder to maintain than a short section of road with a stream crossing. The other plus is that the potable bridge can be removed when the job is complete.

Lack of availability of portable log truck bridges is the main reason they haven’t been used more. The cost of constructing one for one logging contractor is usually prohibitive, because an individual contractor only needs a portable bridge on an occasional basis.

Key tasks that will be included in this project include:

  1. The Logging Educational and Resource Center (LERC) will work with the Northeast and Northwest chapters of the Wisconsin Professional Loggers Association (WPLA) and the Forest Management Systems Cooperative (Minnesota) to ascertain the exact specifications that are needed for their portable bridges.
  2. LERC will contract with Timber Resources, LLC will construct three portable log-truck bridges to the specifications determined in the first task.
  3. Timber Resources will be responsible for contracting any engineering modifications that need to be done to existing designs that Timber resources has.
  4. Timber Resources will construct bridges and develop a method for keeping the bridge parts together and a method for moving major bridge pieces without damage.
  5. Timber Resources will provide a parts list and certified design for each bridge
  6. LERC will develop a sample contract that can be used for each bridge.
  7. The two WPLA chapters and Forest Management Systems Cooperative will take possession of each bridge and make available for use to its members.
Minnesota Department of Natural Resources (MDNR) and the Wisconsin Department of Natural Resources (WDNR) will be involved in the permitting required for installation of these bridges. The bridges themselves will be used on a wide range of ownerships including county forest, state forest, national forest, industrial forestland, and private forestland.

Four portable bridges were constructed, three to be used in Minnesota, one to be used in Northwest Wisconsin. The bridge design was developed by Timber Resources and approved by LERC. To date, the three bridges in Minnesota have been used four times, with two more sites being identified for this summer. The Minnesota bridges have not been used outside of the members in Forest Management Systems Cooperative membership. LERC has developed a contract agreement by which these bridges could be used by anyone with an interest in using them. The bridge in Wisconsin has not been used to date; however, it is scheduled for use this summer.

Each bridge user was asked to fill out an evaluation pertaining to the following topics with these summarized results:

  • Ease of Transport: There was no problem with transportation as there was no need for extra permitting because they are in two parts.
  • Ease of Installation: There was no issue with installation. General installation time was 20 minutes once the beams were in place on either side. Two people were needed for installation, one in the loader and one on the ground.
  • Permitting Process: No permits were required on the four sales tested as they were County Forest sales.
  • Ease of Removal: The removal also posed no difficulty, taking an average time of 10 minutes.
  • Suggestions for Improvements: The only improvement noted was the width of the deck was not wide enough for wide tires on big forwarders.

Contact: Ms. Rachel Zetah, (218) 735-8600


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